Why does a 480 volts 3 phase power supply read 277 across legs?
In: 2
Because 480/sqrt (3) =480/1.73=277
The reason it is sqrt (3)=1.73… is that the 3 phases are 120 deg and VAB is 480, VA and VB is 277. You can just measure the relative lengths and get that the magnitude of a single phase. When you go in reverse you need to divide with it.
You can look at the voltage in [this phasor diagram](https://i.stack.imgur.com/QAGTe.jpg) and VAB is 480, VA and VB is 277. You can just measure the relative lengths and get that relationship.
You can also do the trig in the image and get constant as 2 * cos (30) = sqrt (3)
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